Sunday, 10 May 2015

8 WAYS TO PREVENT BEARING FAILURES

8 WAYS TO PREVENT BEARING FAILURES

We all are well aware that there should be a micro thin
film of lubricant in between rolling element and bearing raceway, in order to
reduce the friction between rolling element and raceway of bearing as well as
to avoid corrosion action over any element of bearing.

So what we will secure here and why should we read this post??

We will try to find out here the mistakes in bearing
lubrication, we must note it that mistakes that we will discuss here might be
avoided if we know the basic of lubrication and with little budget. It is good
for our machine health if we understand the mistakes and the way by which we
can avoid these mistakes.

1.Excess
lubrication

Lubrication is very important for the desired service
life of bearing but we must understand that quantity of grease or oil must not
exceeds the limit as excessive quantity of grease or oil in bearing or in
bearing housing will yield rise in temperature. We may fill the bearing with
grease completely but fill grease in bearing housing to only 1/3rd
portion. Let us consider the case of grease lubricated bearing, when machine
will start filled grease in bearing will be splashed in housing and hence there
must be suitable space for accommodating the splashed grease from bearing
during starting of bearing.

2.Insufficient
lubrication

Insufficient lubrication of bearing is also not
acceptable for the health of our machine bearing. Less quantity of lubricant
(grease or oil as per recommendation) will also yield the rise in temperature
as due to insufficient lubrication there will be metal to metal contact between
rolling element and bearing raceway.

I have observed one case of bearing failure due to
insufficient lubrication, two bearings were fixed at both end of a rotor of a
shredding unit and bearings were oil lubricated, oil leakages were observed
from bearing housing and 200 liters of hydraulic oil 46 were wasted as leak oil
from bearing housing in 8 running hours of machine.

Maintenance crew team decreased the flow of hydraulic oil
to reduce the leak oil but this decision was very danger for the health of
bearing and one bearing out of two bearing was failed due to continuous operation
of machine under insufficient lubrication.

Root cause analysis team have secured the root cause that
drain line of bearing housing was chocked and hence oil was coming through
slightly V grooved oil seals of bearings instead of draining via drain line.
Finally drain line was cleaned and oil seals were replaced with new bearing and
clear instructions were given to team to not reduce the flow of hydraulic oil.

Before replacing oil seal and cleaning drain line, you can’t imagine how much
quantity of hydraulic oil was wasted as leak oil from the system.

3.Application
of lubricant of correct viscosity

Lubricant selection criteria are based over the viscosity
of oil or grease. As maintenance crew member, I am also using same grease as
lubricant for all bearings in our organization. But if we follow the SOP of lubrication,
there is different viscosity grade recommended for ball bearing, spherical
roller bearing and thrust bearing.

Ball bearing: Lubricant grease viscosity 13 cst minimum

Spherical roller bearing: Lubricant grease viscosity 20.6
cst minimum

Thrust bearing: Lubricant grease viscosity 32 cst minimum

We normally use single lubricant for multiple bearing or
for all bearing but we must understand that viscosity of lubricant vary
inversely with temperature that means decreases with rise in temperature and
hence we should not use lower grade viscosity grade lubricant in spherical roller
bearing and thrust bearing.

4.Contamination
in lubricant

Contamination in lubricant (oil or grease) is very
dangerous for service life of bearing similarly as acid for our face. Dust
particle and other foreign particle enter in bearing raceway due to mishandling
of bearing from opening of its cover to fixing with respective shafts. Dust
particle also enters in bearing housing via improper fitted bearing cover or by
damaged lubricant seals and dust particle may enter via grease point made in
bearing housing if grease nipple is not available.

Dust particle deteriorate the rolling element, raceway of
bearing as well as it also help to increase the bearing clearance. Bearing
temperature might be high due to such dust particle; hence we must be careful
during handling, installation and lubrication of the bearings.

5.Oil
seal

As we have studied in above point that dust particles
might enter in to bearing housing and in between bearing rolling element and bearing
raceways. Hence we must use oil seals of good quality such as, rubber metallic
seal, viton seal and garter spring seals.

6.Failure
to inspect the bearing Clearance

We as disciplined maintenance crew team member usually
follow the lubrication frequency as per recommended schedule. According to SKF we
must inspect the bearing after opening its bearing housing cover, cleaning,
recording of bearing radial internal clearance and filling fresh recommended
grease once in year at least.

7.Use
the Correct lubricant

We know oil and grease both are using as lubricant in
industries for various machineries; we must have to use grease and oil as per
manufacturer recommendation only. If manufacturer recommendation is given to
use oil, then we do not have to use grease there.

8.Using
mixed inappropriate lubricant

We must take care during re-lubrication of bearing that
maintenance crew team use similar lubricant as earlier used with that bearing.
Mixing of inappropriate grease, such as sodium based grease and lithium based
grease, reduces the lubrication quality.

Similarly for oil lubricant also, we
should never mix mineral oil with synthetic oil in any case.

Awareness
of lubrication of bearing

We normally attend training and seminars for various technical
agendas such as “how to install bearing correctly”, we must have to trained our
maintenance crew in lubrication also. Lubrication quality and result of
lubrication will only be positive if technicians understand and feel the
importance of lubrication.